I (over at Photosounder.com, home of the program that turns sounds into images and images into sound) have just started a new challenge. It consists in denoising a 115 year old sound by editing its image generated via Photosounder using Photoshop/GIMP/whatever you got or by writing a dedicated image processing algorithm.
The winners get a free license of Photosounder worth $140/€99.
Link to the contest with all the details, examples and files :
Photosounder: Graphical sound denoising challenge